AGREEMENT Pursuant to Rule 13d-1(k)(1) under the Securities Exchange Act of 1934, the undersigned hereby agree that only one statement containing the information required by Schedule 13D (or any amendment thereof) need be filed on their behalf with...

                                                                    EXHIBIT 99.1

                                    AGREEMENT

         Pursuant to Rule 13d-1(k)(1) under the Securities Exchange Act of 1934,
the undersigned hereby agree that only one statement  containing the information
required  by  Schedule  13D (or any  amendment  thereof)  need be filed on their
behalf with  respect to the  beneficial  ownership of any equity  securities  of
Senior  Housing  Properties  Trust,  a Maryland  real  estate  investment  trust
("SNH"), or any subsequent  acquisitions or dispositions of equity securities of
SNH by the undersigned.

October 23, 2001                      HRPT PROPERTIES TRUST



                                      By: /s/ Xxxx Xxxxx
                                      Name: Xxxx Xxxxx
                                      Title: Treasurer and Chief Financial
                                              Officer



                                      REIT MANAGEMENT & RESEARCH LLC



                                      By: /s/ Xxxxxxxx X. Xxxxx
                                          Name: Xxxxxxxx X. Xxxxx
                                          Title:  Vice President and
                                                   Assistant Secretary

                                      REIT MANAGEMENT & RESEARCH TRUST


                                      By: /s/ Xxxxxx X. X'Xxxxx
                                          Name: Xxxxxx X. X'Xxxxx
                                          Title:  Vice President